Metal oxide-hydrogen batteries, such as nickel oxide-hydrogen batteries, have seen use as aircraft starter batteries and in aerospace applications because they are rechargeable, have an extremely long cycle life and provide a uniform output throughout the entire discharge cycle.
In the typical nickel oxide-hydrogen battery, the battery cells are sealed in an outer pressure vessel that contains pressurized hydrogen gas. On discharge of the battery, the hydrogen gas diffuses through the electrolyte surrounding the catalyst surfaces of the negative plates and becomes disassociated to the mono-atomic form. The mono-atomic hydrogen is ionized and combines with hydroxyl ions to form water, with an electron being released in the process of forming each hydrogen ion. In addition, hydroxyl ions are formed at the positive electrode by the reaction of water with the available oxygen content of the nickel oxide. As a result of these reactions, an electron current is produced in the exterior circuit.
On recharging, the reaction is reversed, with the recharging being characterized by the regeneration of hydrogen at the negative electrode and the reoxidation of nickel at the positive electrode.
To withstand the substantial pressures generated by the hydrogen gas, the pressure vessel is generally cylindrical in shape and the practice has been to form the cell modules with a conforming circular configuration. This necessitates cutting curved or circular shaped electrode plates from strips of raw material which results in a high level of expensive scrap.
When using circular cell modules, the electrical connections to the electrodes have normally been at the peripheral edges of the electrode plates. With the electrical connections at the peripheral edge, the electron flow path is lengthened which increases the resistance and reduces the efficiency of the battery.